The present invention generally relates to refrigerated devices having cooled enclosures such as refrigerators and/or freezers. More specifically, the present invention relates to detecting an accumulation of ice on an evaporator associated with the refrigerated device and carrying out a demand defrost operation to remove the ice.
Commercial and domestic refrigerators and freezers are provided with a refrigeration unit for cooling. The refrigeration unit typically has a compressor driven by a compressor motor, a condenser and an evaporator. As the refrigeration unit operates, water vapor condenses on the evaporator and results in the build-up of frost and ice on the evaporator. The build-up of frost and ice on the evaporator results in diminished air flow through the evaporator and a reduction in the ability of the refrigeration unit to cool the air within the refrigerator or freezer. To enhance the efficiency of refrigerators and lower their power consumption, many refrigerators are designed to periodically defrost the evaporator. Defrost devices, such as heaters, are often used to hasten the defrost operation. Also known are refrigerators that defrost on demand by sensing an accumulation of ice and, in response, initiate a defrost operation. Examples of such refrigerators are described in U.S. Pat. Nos. 4,850,204, 4,884,414, 4,916,912, 4,993,233 and 5,666,816, each of which are wholly incorporated herein by reference.
However, the prior art refrigerators fail to teach a demand defrost scheme that uses temperature measurements that are directly related to heat transfer principles as a basis for determining condensate accumulation. Accordingly, the prior art refrigerators have inherent inefficiencies. The prior are refrigerators are also burdened with overly complex algorithms and timing considerations.